Carboxymethyl chitosan-based nanogels via acid-labile ortho ester linkages mediated enhanced drug delivery.

This work described the preparation of two type nanogels based on the crosslinking between carboxymethyl chitosan (CMCS) and two different crosslink agents, an acid-labile cyclic ortho ester compound with dual epoxy end groups (OEDe) or corresponding non-sensitive ethyleneglycol diglycidyl ether (EGDE). The particle size, zeta potential, and micromorphology were characterized by dynamic light scattering and electron microscopy, respectively. Nanogels' stability was also investigated at physiological environments. Doxorubicin hydrochloride as a therapeutic drug model was efficiently embedded into nanogels. The pH-triggered size changing, degradation and drug release were then investigated at three different pH values. Cellular uptake and cytotoxicity evaluation demonstrated that NG1/DOX could be successfully degraded and efficiently release DOX in acid cell organelles, leading to higher cytotoxicity than NG2/DOX. The accumulation and penetration of these DOX-loaded nanogel were then investigated by tumor-like multicellular spheroids (MCTS). The results indicated that the acid-degradable nanogels can deliver more DOX into the inner of MCTS by the hydrolysis of ortho ester bonds, thus efficiently inhibit the growth of MCTS. All results suggested that the acid-degradable nanogels could be degraded in mildly acidic conditions and remain stable at physiological environment, which indicated that the acid-degradable nanogels would be potentially useful as drug carriers.